Apparatus for machining a workpiece of wood, in particular wood beams

ABSTRACT

The drive means (3) is arranged directly on the tool (2) and can be moved together therewith about a plurality of axes (A, B, C and D). The drive means is provided with a tool holding means for automatically delivering or receiving tools in a tool magazine (5) which is arranged above the region of operation of the tool (2). In that way a plurality of tools can be operated with a single drive means, wherein the tool guidance, workpiece forward feed and interchange of tools can be fully automated and programmed.

This is a division of application Ser. No. 116,081 filed November 3,1987.

The invention relates to an apparatus for machining a workpiece of wood,in particular wood beams.

For the rational machining of wood beams and joists, apparatuses arealready known in which the beams, mounted on a roller stool,successively pass through various machining stations, a respectivemachining tool being arranged at each station. Thus the beams may be cutto length for example at a first station, milled at a second station andbored at a third station. The known apparatuses operate in acomparatively non-rational fashion as a great deal of time is requiredfor setting up the machines and the individual working operations can beautomated only to a very limited extent. However modern civilengineering with wood requires some machining operations in whichautomation would be desirable in order to reduce the overall costsinvolved. Thus for example, for building a lattice structure or trussassembly the ends of wood beams must be slotted and bored for receivingconnecting elements.

An object of the present invention is therefore to provide an apparatusof the kind set forth in the opening part of this specification, withwhich workpieces of wood can be machined in a versatile manner in anextremely rational fashion, wherein the machining operations can beextensively pre-programmed.

Another object of the invention is in particular to provide a drivemeans which permits the tool to be fixed directly on the drive shaftwithout unnecessary transmission arrangements.

In accordance with the invention that object is achieved by a drivemeans for a machining apparatus comprising an electric motor having acasing which contains a rotor and a stator, and a drive shaft mounted inthe casing, which drive shaft extends from both sides of the rotor andwhich is provided at one end with a receiving means for force-lockinglyreceiving a tool, the receiving means having an entrainment disccoaxially mounted with the drive shaft outside of the casing, whereinthe entrainment disc can be arrested within the resting pin which canengage into a recess in the entrainment disc in a predetermined positionof the entrainment disc, and including means for moving the arrestingpin into engagement with the recess, and wherein a rest position of theentrainment disc can be detected by a sensor which is stationaryrelative to the entrainment disc, and the arresting pin is activatableonly when a rest position has been detected.

As the tool, together with the drive means, can be moved in differentaxes in the forward feed region of the transport means, no troublesometransmission arrangements such as for example cardan shafts, chains andthe like are required between the drive means and the tool. The drivemeans is itself provided with a tool holding means, which increases theoptions for operation of the tool. The tool magazine which is arrangeddirectly over the region of operation of the tool permits rapidautomatic interchange of the tools. After a given working operation isconcluded, such as for example cutting the beam to length by means of asaw blade, the saw blade can be replaced by a drill within a few secondsso that the apparatus is ready for a fresh machining operationimmediately, almost without any stoppage times. All the operatingmovements involved can be freely programmed so that even complicatedmachining shapes such as for example milled contours and the like arepossible.

Particularly versatile and comprehensive machining modes are provided ifthe drive means is fixed to a cantilever arm which is displaceable in aplane transversely with respect to the direction of forward feed of thetransport means in vertical and horizontal directions and if the drivemeans is also rotatable about the axis of the arm and about an axistransversely with respect to the axis of the arm. Together with suitableprogramming of the forward feed movement and with a corresponding numberof tools in the tool magazine, almost any desired cutting machiningoperations can be carried out in that way.

The tools in the tool magazine may be changed in a particularly simplefashion if the tool magazine has a holding rack which is arrangedsubstantially parallel to the cantilever arm, with tool holders arrangedin a row, and if the holding rack is displaceable relative to the armfor receiving and delivering the tools. In that case, in the actual toolchange operation, the drive means moves into a given zero or neutralposition and actuates only the tool holding means. The tool is loadedand unloaded by displacement of the tool holders to which the individualtools are clamped fast.

The forward feed movement of the workpieces may be produced in aparticularly advantageous manner if the transport means has at least onerail-mounted clamping carriage with a support surface for the workpiece,and the workpiece can be acted upon by a clamping force in the plane ofthe support surface and transversely with respect to that plane, bymeans of respective separate clamping means. The dual clamping optionpermits the workpieces to be positioned in the optimum fashion. Incertain machining processes, it is also possible to operate with onlyone clamping means.

Machinability of the workpieces can be further facilitated if theworkpiece can be acted upon, transversely to the plane of the supportsurface, by a clamping means having a clamping bar which can be pivotedopen and whose pivot point lies on one side of the support surface. Theclamping bar can thereby be activated only for positioning of the woodbeams. The clamping bar is then pivoted open and the workpieces are onlyheld by the second clamping means which clamps them in the plane of thesupport surface. By virtue of that arrangement the beams can be freelymachined on their top over their entire length, even if the beams lie ona plurality of clamping carriages.

As the tools are fixed directly on the drive shaft of the drive means,the latter must be of a special design so as to permit automatic toolchanging. That tool changing operation may be carried out in a quiteparticularly advantageous fashion if the drive means is an electricmotor with rotor and stator and a drive shaft which is mounted in acasing, wherein the drive shaft is in the form of a hollow shaft whichextends on both sides by way of the rotor and which is provided at oneend with a receiving means for force-lockingly receiving a tool, and ifarranged in the hollow shaft is a gripping means for retaining a tool inthe receiving means. In that way the drive shaft performs a doublefunction insofar as it not only provides the torque required foroperation of the tool, but it also permits automatic interchange of thetools.

In per se known manner the receiving means comprises an entrainment discwhich is disposed around an inside cone member for receiving a Morsetaper member, the gripping means having a clamping claw which is fixedto a clamping rod and which can be actuated by axial displacement of theclamping rod in the hollow shaft. The clamping claw is thus disposed inthe interior of the motor and may be easily opened by way of theclamping rod.

The clamping rod may be actuated in a particularly simple manner if aspring means is arranged at the end of the hollow shaft which is inopposite relationship to the receiving means, the spring means engagingthe clamping rod and being adapted to bias the clamping rod in such away that the clamping claw can be opened only against the spring force.The spring means increases the overall length of the motor only slightlyin that manner and in addition may be easily disposed in the casing ofthe motor. The spring means may be operated in a particularly simplefashion if arranged on the casing is a pressure fluid cylinder whosepiston is arranged coaxially with respect to the clamping rod and withwhich the clamping rod is displaceable against the force of the springmeans in the hollow shaft. When the piston is in a non-loaded condition,the clamping rod is thus always biased by the spring means. The pistonhas to be briefly actuated only for the purposes of changing the tools,in order thereby to displace the clamping rod. That arrangement isparticularly simple and reliable in operation. The parts which rotatewith the drive shaft are reduced to a minimum.

The receiving means can be cleaned by means of compressed air in aparticularly simple fashion by both the clamping rod and also the pistonbeing provided with a coaxial bore, wherein the two bores communicatewith each other when the piston is in a condition of pressing againstthe clamping rod, with the bore on the piston being connected to acompressed air source for blowing out the receiving means. Thatarrangement does not require any sealing action in respect of rotatingcomponents as in fact the compressed is only blown into the clamping rodwhen the drive shaft is stationary.

For the automatic tool change operation, the entrainment disc must bemoved into a given position so that the entrainment pins or entrainmentbars which are provided on the tool engage into the entrainment disc.The entrainment disc may be positioned in a particularly advantageousmanner if it can be arrested by means of an arresting pin which isengageable into a recess in a predetermined position of the entrainmentdisc. When the arresting pin is in the engaged condition, that ensuresthat the receiving means receives the tools in the tool magazine in thecorrect position. The arresting pin is preferably disposed on a pistonwhich is displaceable in a pressure fluid cylinder integrated into themotor casing. Actuation of the arresting pin can thus be remotelycontrolled in a particularly simple manner. A particular smooth andcareful arresting action can be achieved if the rest position of theentrainment disc can be detected by a sensor which is stationaryrelative to the entrainment disc, and if the arresting pin can beactivated only when the rest position has been detected. In thatsituation, the procedure involved is particularly advantageously suchthat firstly the motor is decelerated until the sensor signals the restposition of the entrainment disc. The arresting pin is then pressedunder a biasing force against the entrainment disc, irrespective of theposition in which the entrainment disc is to be found. Finally the motoris further activated for a brief period until the arresting pin engagesinto the recess on the entrainment disc. Even when using heavy toolswith a relatively high degree of inertia, that procedure does not resultin excessive loadings on the entrainment disc and the arresting pin.

An embodiment of the invention is described in greater detailhereinafter and illustrated in the drawings in which:

FIG. 1 is a perspective view of an apparatus according to the invention,

FIG. 2 is a plan view of the apparatus of FIG. 1,

FIG. 3 is a front view of a single clamping carriage,

FIG. 4 is a side view of the clamping carriage shown in FIG. 3,

FIG. 5 is a view in cross-section on the plane I--I in FIG. 3,

FIG. 6 is a view in cross-section through a drive means,

FIG. 7 is a perspective view of the gripping means in the opened and theclosed positions, and

FIG. 8 is a plan view of an entrainment disc.

As shown in particular in FIGS. 1 and 2, a plurality of wood beams 1 areclamped on individual carriages 9. The clamping carriages aredisplaceable along an upper rail 37 and a lower rail 38 in the directionindicated by the arrow F. The actual machining center is disposed in aprotective housing 31 which is shown in FIG. 1 in a partly cut-away formand in entirely cut-away form in FIG. 2.

An opening 32 is provided in the housing 31 on both sides so that theclamping carriages 9 can be passed through the protective housing 31.The two rails 37 and 38 extend over approximately the same length onboth sides of the protective housing 31 so that it is possible tooperate on alternate sides. While the beams are being fed to the toolfrom one side, a new layer of beams can be laid on to and positioned onthe clamping carriages on the opposite side. That means that there arepractically no stoppage times involved in loading the machine.

The tool itself is secured directly to a drive means 3 which will bedescribed in greater detail hereinafter. The drive means is fixed to acantilever arm 6 which is horizontally displaceable in the directionindicated by the arrow A. In the vertical direction, the entire arm 6can be displaced in the direction indicated by the arrow B on a stand 33so that the tool 2 can reach any desired co-ordinates in a planetransversely with respect to the direction of forward feed movement asindicated at F, within a given area. A vertical spindle 34 and ahorizontal spindle 35 are provided for displacing the arm 6 in the twodirections of movement. The two spindles are surrounded by atelescopically compressible sheathing to protect them from fouling. Thetwo spindles 34 and 35 can be precisely rotated to fractions of arevolution by means of electric motors, the control devices required forthat purpose being known to the man skilled in the art.

The drive means 3, together with the tool 2, may also be rotated in thedirection indicated by the arrow C about the horizontal axis of movementof the arm 6 and in addition in the direction indicated by the arrow Dabout an axis which is transverse with respect to that axis of motion.In that way a tool 2 can be moved practically into any desired inclinedposition transversely with respect to the plane of movement of the arm6. It will be appreciated that, in the case of certain machiningoperations, for example in an inclined cutting operation, the movementof the tool 2 is to be co-ordinated with the forward feed movement ofthe clamping carriages 9, but that can be readily achieved by a suitablecontrol arrangement, by way of a computer.

A tool magazine 5 is arranged above the region of operation of the tool2. The tool magazine 5 includes a holding rack 7 with individual toolholders 8. The tool holders are provided with clamps into which thetools can be engaged by means of their tool shank. The holding rack 7 isdisplaceable by means of a pressure fluid cylinder 42 in the directionindicated by the arrow E, that is to say relative to the plane of motionof the arm 6. In order to protect the tool magazine 5 from wood dust andchips in a machining operation, a curtain 36 extends at least over thelower side of the tool magazine. The curtain 36 is preferably in theform of a roller blind which can be rapidly displaced with a drivemeans. The operation of changing a tool in the tool magazine 5 takesplace in the following fashion: as soon as a machining operation with agiven tool is concluded, the drive means 3 is automatically moved into agiven loading position. In that loading position the tool 2 is disposedwith its shank in the same plane as the holding rack 7. The tool 2 isnow moved into a position beneath that tool holder 8 to which thecorresponding tool belongs and which is now empty. The curtain is openedand the arm 6 is raised in the direction indicated by the arrow B untilthe tool shank engages into the corresponding tool holder. The toolholding device in the drive means is now released so that the tank ofthe tool is freed. The entire holding rack with the tool which has justbeen used can now be moved back in the direction indicated by the arrowE. That is necessary in order to give the arm 6 the necessary freedom ofmotion in the direction indicated by the arrow A so that it can be movedinto a position in which the axis of the drive means is coaxial with theaxis of the tool which is to be freshly picked up in the holding rack 7.The holding rack 7 is now again moved towards the arm 6 in the directionindicated by the arrow E until the tool which is to be freshly picked upengages into the tool holding device on the drive means 3. The arm 6 cannow be moved downwardly in the direction indicated by B, with thefreshly picked-up tool being released from the tool holder 8 thereof.Directly after leaving the tool magazine 5, the curtain 36 is closedagain.

Arranged on the ground in the protective housing 31 beneath the regionof operation of the tool 2 is a conveyor belt 41 on which wood waste istransported away. A discharge arrangement for sucking away wood dust andsmaller particles of wood is preferably also disposed in the interior ofthe protective housing 31, as is already the usual practice inconventional wood machining machines.

The construction and the mode of operation of the individual clampingcarriages 9 will now be described with reference to FIGS. 3 to 5. Asalready mentioned above, the carriages 9 can be displaced along an upperrail 37 and a lower rail 38 which in the present case are in the form ofa double-T-beam. The two rails are carried by vertical supports 44 whichare arranged at regular spacings. It will be appreciated however thatanother rail construction would also be possible. Thus for example tworails on which the carriages 9 are displaceable could also be arrangedon the ground. However the illustrated construction has the advantagethat no structural arrangements whatever are required on the ground andthe surface beneath the wood beams 1 carried on the carriages remainsfully accessible so that for example a fork lift truck can move into theregion of movement of the carriages 9.

The wood beams 1 to be machined lie on a horizontal carrier 43 whichforms a support surface 10. The carrier is secured to two mutuallyfacing U-shaped members 55 which extend in parallel relationship in avertical direction. The members 55 are in turn secured at their ends tohorizontal rectangular member 54 which carry the rail mounting 45.Arranged at the outer free end of the carrier 43 is a clamping means 11with which the wood beams 1 can be clamped in the horizontal direction.The clamping means 11 can be engaged into bores which are arranged atcertain spacings over the entire length of the carrier 43. In that wayit is possible to take account of the width of the bundle of beams or itis even possible for a plurality of clamping devices to be fitted on acarrier.

The two U-shaped members 55 serve at the same time as mountings for apair of sliding members 56 which are displaceable in the U-shapedmembers in a vertical direction. The pair of sliding members 56 areconnected together by vertical connecting members 65, the lower one ofwhich is mounted in a lift spindle 46. The spindle 46 can be driven bymeans of a lift motor 47 so that the entire unit consisting of themembers 56 and the connecting members 65 is adjustable in respect ofheight in the U-shaped members 55.

A clamping beam or bar 12 is mounted pivotably about a pivot axis 49 inthe upper region of the slide members 56. A crank lever 51 is arrangedat a right angle to the clamping bar 12. The lever 51 can be actuated byway of a special link mechanism by means of a hydraulic cylinder 48which is pivotally carried on a support 50 on the lower connectingmember 65. The link mechanism is shown in greater detail in particularin FIG. 5. It comprises a short link member 52 and a long link member 53which are connected together at the shaft 57. The piston rod of thehydraulic cylinder 48 also pivotally engages the shaft 57. The shortlink member 52 is connected to the free end of the crank lever 51 at thepivot shaft 61. The long link member 53 is pivotally connected to asupport 58 at the pivot shaft 60. The support 58 is in turn secured tothe pair of slide members 56.

It will be seen that, for pivoting the clamping bar 12 upwardly in thedirection indicated by the arrow H, the hydraulic cylinder 48 must beactivated in such a way that the piston rod thereof is moved in thedirection indicated by the arrow J. The link members 52 and 53 which aredisposed in one plane fold in downwardly and the pivot shaft 57 rotatesabout the stationary pivot shaft 60 on the support 58. The carrier 43 ispreferably fitted with the wood beams 1 when the clamping bar 12 ispivoted upwardly. The wood beams 1 are partially distorted or warped andmust therefore be subjected by a suitable clamping means to a pressingforce acting in the vertical direction. For that purpose the hydrauliccylinder 48 is activated in the opposite direction until it in turnoccupies the horizontal position shown. In that case the two linkmembers 52 and 53 and in particular the pivot axes 60, 57 and 61 thereofalso lie in a horizontal plane. The motor 47 is now operated so that theclamping bar 12 which is fixed to the slide members 46, together withthe hydraulic cylinder 48, moves downwardly in the direction indicatedby the arrow K on the spindle 46 until the clamping bar bears againstthe wood beams. In that position, for the purposes of applying theactual clamping force, a hose 71 is pumped up with pressure fluid, beingarranged on the underside of the clamping bar 12 and extending over theentire length thereof. In that way the beams 1 are pressed against thesupport surface 10 of the carrier 43. It will be appreciated that thevertical pressing force could also be applied in some other fashion. Theparticular advantage of the described link arrangement is that thetorque which occurs at the free end of the crank lever 51 is nottransmitted to the hydraulic cylinder 48 but to the support 58. Only acomparatively low pressure is required at the hydraulic cylinder 48 tohold the two link members 52 and 53 in the horizontal position. In thatway the hydraulic cylinder 48 is not loaded even in the event of highpressing forces on the clamping bar 12. There also cannot be any springaction caused by compressibility of the pressure medium.

Depending on the way in which the wood beams 1 are to be machined, theclamping bar 12 can be pivoted upwardly again after the pressingoperation so that the wood beams 1 are only clamped and retained inposition in a horizontal direction by the clamping means 11. As a resultof that, the entire top side of the wood beams 1 remains free for amachining operation. The clamping carriages 9 are displaced along a rack39 on the upper rail 37 by means of a motor (not shown).

The drive means for the tool 2 is shown in greater detail in FIG. 6. Itessentially comprises a squirrel-cage rotor electric motor comprising arotor 13 disposed in a casing 15, with a stator 14. The rotor and thestator are of a relatively slender elongate configuration in order tominimize the diameter of the motor to the greatest possible extent. Itwill be seen that, the smaller the overall motor diameter, the greateris the useful depth of a tool, for example a circular saw blade. Thedrive shaft of the motor is in the form of a hollow shaft which ismounted in the casing 15 in rolling bearings 66. The hollow shaft 16 isprovided at one end with a tool holding means 4 which force-lockinglyholds the tool 2. With the high speeds of rotation required on woodmachining machines, there is no need for a special transmission stage.The speed of rotation of the motor can be regulated by way of itsfrequency, in per se known manner.

The tool holding means 4 essentially comprises an entrainment disc 17and an inside cone member 18. The wood machining tools have a steeptaper member 19 with diametrally oppositely disposed entrainment grooveswhich are arranged at given standard dimensions. The taper member 19fits positively into the inside cone member 18 and the diametrallyoppositely disposed keys 68 which are fixed to the entrainment disc 17and the hollow shaft 16 respectively engage into the entrainment groovesin the taper member 19. The two keys 68 lie in the key tracks 67 and arescrewed fast in position therein, as can be seen from FIG. 8 which onlyshows the key tracks with the screwthreaded bore. Screwed into the tapermember 19 is a clamping pin 69 on which the taper member 19 can bepulled into and retained in the inside cone member 18.

A clamping rod 20 is axially displaceably mounted in the hollow shaft16. Fixed to one end of the clamping rod 20 is a clamping claw 21 whichis radially biased in such a way that it opens as soon as the clampingrod 20 is moved in the direction indicated by the arrow L towards theinside cone member. When the taper cone 19 is fitted, the clamping clawcan engage the clamping pin 69 in that way. When the clamping rod 20 isactuated in the opposite direction, the clamping claw closes and pullsthe taper member 19 into the inside cone member 18.

For the purpose of clamping the clamping rod 20, the arrangement has aspring assembly 22 which is arranged at one end of the hollow shaft 16and which engages the clamping rod 20. The spring assembly 22 comprisesa sandwich-like assembly of diaphragm springs and is so dimensioned thatthe tool 2 cannot come loose from the tool holding means 4 even whenhigh axial forces are involved.

For the purposes of opening the clamping claw 21 or for displacing theclamping rod 20 in the direction indicated by the arrow L, thearrangement has a piston 24 arranged coaxially with the clamping rod 20in a pressure fluid cylinder 23. The cylinder 23 has a pressure fluidconnection 63 on one side and the piston 24 is biased by a spring 70 sothat in the non-loaded condition it occupies the position shown in thedrawing. In that position the piston 24 is not in contact with theclamping rod 20 so that the entire force of the spring assembly 22 actson the clamping rod 20. If the tool 2 is to be removed from the toolholding means 4, the piston 24 is operated so that it displaces theclamping rod 20 in the direction indicated by the arrow L against theforce of the spring assembly 22. When that happens the clamping claw 21is opened and releases the clamping pin 69, as shown in FIG. 7.

Both the piston 24 and also the clamping rod 20 are provided with acoaxial bore 25, the bores communicating with each other when the piston24 is pressed against the clamping rod 20. The bores 25 serve to blowout the tool holding means with compressed air in each tool changeoperation, and in that way to clean it of saw dust and the like.

For the purpose of automatic tool pick-up, the entrainment disc 17 mustalways be moved into the same position so that the entrainment keys 68engage into the entrainment grooves in the taper member 19. Thatpositioning operation is performed by means of an arresting pin 26 and asensor 30, which are both arranged on the motor casing in the region inwhich the entrainment disc 17 moves. The arresting pin is fixed to apiston displaceable in a pressure fluid cylinder 29. The cylinder 29 ispreferably integrated into the motor casing and is supplied by way of apressure fluid connection 64. Preferably, that unit is a pneumaticallyoperable piston which is also biased by means of a spring 72. In thenon-loaded condition, as shown in the drawing, the arresting pin 26 isretracted so that the entrainment disc can rotate freely. The sensor 30serves to sense stopping or rotation of the entrainment disc or a quitespecific position thereof. The entrainment disc 17 can be arrested bythe arresting pin at recesses 27 which in the present embodiment alsoserve for signal formation purposes for the sensor 30. The sensor 30 isan electromagnetic probe which detects whether a recess 27 is or is notto be found in the region of the probe. It will be appreciated that thesensor 30 could also be an optical probe which senses a light-dark codeon the entrainment disc 17.

In the above-mentioned operation of automatically changing a tool, thefollowing procedure takes place in the drive means: the motor isdecelerated until the sensor 30 signals that the entrainment disc 17 isstopped. In that case the entrainment disc 17 remains stationary in anyposition so that the sensor 30 signals either only dark or metal or onlylight or non-metal. After the entrainment disc has been detected asbeing stopped, the pneumatic piston 28 is operated so that the arrestingpin 26 is pressed against the entrainment disc 17 by a biasing force. Ifthe recess 27 is by chance precisely in the right position, thearresting pin 26 engages thereinto and no further positioning step isthen required. If however one of the two recesses 27 is not aligned withthe arresting pin, the motor is briefly operated again until the sensor30 signals a recess 27. The biased arresting pin 26 now immediatelyengages into the oppositely disposed recess so that the entrainment disc17 cannot be rotated any further.

After the operation of positioning the entrainment disc has been carriedout, the piston 24 is operated in the above-indicated manner so that theclamping claw 21 opens. When that happens, at the same time compressedair is blown into the tool holding means by way of the bores 25. Thetool with its taper member 19 can now be removed from the inside conemember 18. A fresh tool is then inserted into the tool holding means 4,the entrainment grooves thereof being disposed in precisely the sameposition as the tool which has just been removed. The pressure fluidcylinder 23 is now relieved so that the clamping rod 20 is in turnsubjected to the force of the spring assembly 22 and the clamping claw21 closes. At the same time the feed of compressed air for blowing outthe tool holding means is cut off. The pneumatic cylinder 29 is thenrelieved so that the arresting pin 26 is urged out of the recess 27 bythe spring 72. The drive means is now ready for operation again. It willbe seen that the extremely slender and short design configuration of thedrive means provides a large region of operation in respect of the tool2. That concerns on the one hand the depth of cut of the tool and on theother hand the rotatability of the drive means in the directionsindicated by the arrows C and D in FIG. 1, with the shortest possibleradius.

I claim:
 1. A drive means for a machining apparatus comprising anelectric motor having a casing which contains a rotor and a stator, anda drive shaft mounted in the casing, the drive shaft being in the formof a hollow shaft which extends from both sides of the rotor and whichis provided at one end with a receiving means for force-lockinglyreceiving a tool, a gripping means disposed in the hollow shaft forretaining a tool in the receiving means, said gripping means comprisinga clamping claw which is fixed to a clamping rod which can be actuatedagainst the force of a spring means by axial displacement of theclamping rod in the hollow shaft to open the clamping claw, a pressurefluid cylinder whose piston is arranged coaxially with respect to theclamping rod for axially displacing the clamping rod, wherein both theclamping rod and the piston are provided with a coaxial bore such that,when the piston is pressing against the clamping rod, the two borescommunicate with each other, and the bore in the piston being connectedto a compressed air source for blowing out the receiving means via thebore in the clamping rod, said receiving means including an entrainmentdisc which surrounds an inside cone member for receiving a Morse tapermember, the entrainment disc being arrestable with an arresting pinwhich can engage into a recess in the entrainment disc in apredetermined position of the entrainment disc, and including means formoving the arresting pin into engagement with the recess, and wherein arest position of the entrainment disc can be detected by a sensor whichis stationary relative to the entrainment disc, and the arresting pin isactivatable only when a rest position has been detected.
 2. A drivemeans according to claim 1 characterised in that arranged on the end ofthe hollow shaft which is in opposite relationship to the receivingmeans is said spring means which engages the clamping rod and with whichthe clamping rod is biased in such a way that the clamping claw can onlybe opened against the spring force.
 3. A drive means for a machiningapparatus comprising an electric motor having a casing which contains arotor and a stator, and a drive shaft mounted in the casing, which driveshaft extends from both sides of the rotor and which is provided at oneend with a receiving means for force-lockingly receiving a tool, saidreceiving means having an entrainment disc coaxially mounted with saiddrive shaft outside of said casing, wherein said entrainment disc can bearrested with an arresting pin which can engage into a recess in theentrainment disc in a predetermined position of the entrainment disc,and including means for moving said arresting pin into engagement withsaid recess, and wherein a rest position of the entrainment disc can bedetected by a sensor which is stationary relative to the entrainmentdisc, and the arresting pin is activatable only when a rest position hasbeen detected.
 4. A drive means according to claim 3 characterised inthat the arresting pin is arranged on a piston which is displaceable ina pressure fluid cylinder which is integrated into the casing and whichcomprises said means for moving said arresting pin.
 5. A method ofpositioning an entrainment disc on the shaft of a drive motor accordingto claim 3 characterised in that firstly the motor is decelerated untilthe sensor signals a rest position of the entrainment disc, that thenthe arresting pin is pressed under a biasing force against theentrainment disc, and that the motor is briefly activated again untilthe arresting pin engages into the recess.
 6. Apparatus as claimed inclaim 3 wherein said drive shaft is a hollow shaft, and including agripping means disposed in the hollow shaft for retaining a tool in thereceiving means, said gripping means comprising a clamping claw which isfixed to a clamping rod which can be actuated against the force of aspring means by axial displacement of the clamping rod in the hollowshaft to open the clamping claw, and a pressure fluid cylinder foraxially displacing the clamping rod.
 7. Apparatus as claimed in claim 3wherein said entrainment disc surrounds an inside cone member forreceiving a Morse taper member.